1. Field of the Disclosure
The present disclosure relates to a trip device for a circuit breaker, and particularly, to a trip device using a bimetal as a trip element.
2. Background of the Disclosure
Generally, molded case breaker circuits are a type of electronic device that manually switches on or off an electric circuit by using a handle, or when a fault current such as a short circuit current occurs, detects the fault current to automatically break the electric circuit, thereby protecting a load device and the electric circuit.
FIG. 1 is a cross-sectional view illustrating a related art circuit breaker. FIG. 2 is a perspective view illustrating an indirect trip device of FIG. 1. FIG. 3 is a perspective view illustrating a related art direct trip device for a circuit breaker.
As illustrated in FIGS. 1 to 3, a related art circuit breaker includes a case 10, a fixed contact 20 that is fixedly disposed at the case 10, a moving contact 30 that is disposed to be contactable with and detachable from the fixed contact 20, a switching mechanism 40 that switches on or off the moving contact 30, and an instant trip device 60 that, when a fault current such as a short circuit current occurs, detects the fault current and automatically triggers the switching mechanism 40 in order for the switching mechanism 40 to move to a tripping position within a momentary time. The switching mechanism 40 includes a handle 50 for manually switching on or off the switching mechanism 40 and a crossbar 42 that performs a function (a trigger function) of binding a latch (not shown) of the switching mechanism 40 and releasing the binding of the latch when a below-described bimetal 62 is bent.
Generally, trip devices are categorized into direct trip devices, which directly generate heat with a current flowing in a bimetal, and indirect trip devices which are heated by a heater which is a separate heat generating member. The trip device of FIG. 1 is the indirect trip device 60. The indirect trip device 60, as illustrated in FIG. 2, includes a first terminal 66 which is connected to a power source circuit or a load circuit at one side of the first terminal 66 and is connected to a heater 64b of a below-described second terminal 64 at the other side, the second terminal 64 which is connected to the power source circuit or the load circuit at one side of the second terminal 64 and is connected to the first terminal 66 through the heater 64b at the other side, and the bimetal 62 which is coupled to the second terminal 64 to be opposite to the heater 64b. The bimetal 62 is heated by the heater 64b, and thus, a temperature increases, whereby the bimetal 62 is bent in one direction.
Due to such a configuration, when a fault current is conducted, a current flows between the first terminal 66 and the second terminal 64, and the heater 64b generates heat with the current. The heater 64b heats the bimetal 62 with the generated heat. The heated bimetal 62 is bent in a right direction in FIG. 2. The bent bimetal 62 rotates the crossbar 42 by using the pressure member 62a to bind a latch (not shown) of the switching mechanism 40 and release the binding of the latch. When the binding of the latch (not shown) is released, the moving contact 30 is quickly detached from the fixed contact 20 by an elastic force of a trip spring (not shown) of the switching mechanism 40.
Here, the indirect trip device 60 uses a method in which the bimetal 62 does not directly generate heat, and the heater 64b that is the separate heat generating member generates heat to heat the bimetal 62. Therefore, the indirect trip device can prevent the bimetal 62 from being damaged by a fault current, and thus is applied to a circuit breaker for a high rated current.
FIG. 3 illustrates a direct trip device 60′. The direct trip device 60′ includes a first terminal 66′ which is connected to a power source circuit or a load circuit at one side of the first terminal 66′ and is connected to one side of a bimetal 62′ through a lead wire 66c′ at the other side, a second terminal 64′ which is connected to the power source circuit or the load circuit at one side of the second terminal 64′ and is connected to the other side of the bimetal 62′ at the other side, and the bimetal 62′ which is coupled to the lead wire 66c′ of the first terminal 66′ at one side of the bimetal 62′ and is connected to the second terminal 64′ at the other side. When electricity is conducted, a current flows in the bimetal 62′, and thus, the bimetal 62′ directly generates heat, whereby the bimetal 62′ is bent.
Due to such a configuration, when a fault current is conducted, a current flows from the second terminal 64′ to the first terminal 66′ through the bimetal 62′. At this time, the bimetal 62′ directly generates heat. A temperature of the bimetal 62′ increases due to the directly generated heat, and thus, the bimetal 62′ is be bent in a right direction in FIG. 3. The bent bimetal 62′ rotates the crossbar 42 by using a pressure member 62a′ to bind the latch (not shown) of the switching mechanism 40 and release the binding of the latch. When the binding of the latch (not shown) is released, the moving contact 30 is quickly detached from the fixed contact 20 by an elastic force of the trip spring (not shown) of the switching mechanism 40.
Here, the direct trip device 60′ uses a method in which a current flows in the bimetal 62′, and thus, the bimetal 62′ directly generates heat. Therefore, despite a low rated current, the direct trip device 60′ generates a large amount of heat, and thus is applied to a circuit breaker for a low rated current.
However, an amount of heat generated by the related art indirect trip device 60 for a circuit breaker is insufficient under a low rated current, and thus, a bending amount of the bimetal 62 is insufficient. For this reason, the related art indirect trip device 60 cannot detect a fault current. Also, in the related art direct trip device 60′ for a circuit breaker, the bimetal 62′ can be damaged by a fault current.